To gain the perk, the Sole Survivor has to reach maximum affinity with Curie, which is possible after completing her personal quest (Emergent Behavior). She will then tell the player character about how she made a breakthrough with mutfruit that enhances the effect of stimpaks.
Once a day the player character can heal 100 Hit Points if their current number of Hit Points is below 10%.
PC This perk does not work due to a coding error that makes it trigger at 10.0 or 1000% health instead of at 0.1 or 10%. [verified] The Unofficial Fallout 4 Patch mod corrects this coding error.